This invention relates to approaches for depositing chemical compositions on substrate in solution form. The invention is particularly suited for depositing solution to be dried on substrate for use in producing reagent test strips.
Analyte detection assays find use in a variety of applications including clinical laboratory testing, home testing, etc., where the results of such testing play a prominent role in the diagnosis and management of a variety of conditions. The more common analytes include glucose, alcohol, formaldehyde, L-glutamic acid, glycerol, galactose, glycated proteins, creatinine, ketone body, ascorbic acid, lactic acid, leucine, malic acid, pyruvic acid, uric acid and steroids. Analyte detection is often performed in connection with physiological fluids such as tears, saliva, whole blood and blood-derived products. In response to the growing importance of analyte detection, a variety of analyte detection protocols and devices for both clinical and home use have been developed. Many detection protocols employ a reagent test strip to detect analyte in a sample.
In producing reagent test strips, one or more stripes of reagent is typically applied to a substrate and dried. The substrate often comprises a continuous web of material proceeding from a coating station, passing reagent drying features and take up on a roll. Coated substrate is often then associated with other elements and singulated to produce individual test strips. In this production scheme, an area of particular importance lies in suitable application of reagent to the substrate.
This is important for a number of reasons, ranging from economic considerations to safety. Clearly, precision in laying-down reagent will result in less waste of material that is often costly. Further, an ability to consistently lay down reagent coating will provide for test strips delivering more consistent results, better enabling appropriate response by a user or a physician.
Whether used in producing reagent test strips or otherwise, the present invention is more able to produce consistent and controlled solution striping than existing coaters. Existing coaters-over which the present invention offers improvement-include, grooved roller arrangements and examples as presented in British Pat. No. 384,293; Canadian Pat. No. 770,540; Russian Pat. No. 413,053; and U.S. Pat. Nos. 3,032,008, 3,886,898 and 4,106,437.
According to the text of the ""437 patent, each of the other referenced approaches encounter difficulties in achieving precise control of stripe width and registration. Further, they are characterized as unduly complex and/or difficult to maintain.
While the device in the ""437 patent is said not to suffer such drawbacks and to be capable of carrying out multiple stripe coating of a web at high speeds and with a high degree of precision, much greater precision has been observed in practicing the present invention when depositing very low viscosity solutions. Furthermore, in using low viscosity solutions, the present invention is more forgiving with respect to setup, tolerating greater inconsistency in spacing between the substrate to be coated and the point(s) of solution delivery from the die. Also, the present invention offers a far more durable solution since fragile extension from the die are not employed.
Another die for slot coating produced by Troller Schweizer Engineering Ag (Murganthal, Switzerland) is more similar to the present invention in some respects than the die described in the ""437 patent. Due to certain structural similarities, comparable performance in stripe width deposition may be obtained when set up properly. However, die setup is often difficult due to the layered construction of the device. Even when set up properly though, the use of vertically-oriented sections in the die introduce significant leakage problems in coating substrate with low viscosity solution. Especially where costly reagent materials are concerned, such leakage is clearly economically disadvantageous. Leakage also introduces another variable in solution management making it more difficult to lay down consistent width and thickness stripes or bands of solution.
Prior to the present invention, in particular the challenges associated with slot coating low viscosity solutions were not appreciated. As the invention itself is the first known application of slot coating technology to low viscosity solutions in the range of 0.50 to 5.0 centipoises, the problems solved by features described herein were appreciated only in connection the present invention. While the ""437 patent is silent to what viscosity solution may be employed with the die, it cites examples of typically higher viscosity fluids including solutions or dispersions of polymeric material containing a die or pigment, magnetic dispersions, phosphor dispersions, radiation-sensitive photographic emulsions and adhesive compositions. Troller dies most often find use in laying down viscous inks, pastes and plastics.
Accordingly, the present invention provides a significant advance in precision solution coating, especially with low or very low viscosity solutions. Those with skill in the art may well appreciate further advantages or possible utitlity in connection with the features herein. Whatever the case, it is contemplated that some variations of the invention may only afford certain advantages, while others will present each of them.
Features of the invention provide for accurate coating of material with bands or stripes of solution with a slot coating die. Often, the substrate material comprises webbing passed by the specially-configured die. The webbing may be supported on a backing roller to locate the webbing in close proximity to the front of the inventive die. To deposit solution on the webbing in one or more stripes or bands, solution under pressure is extruded or pushed out of the die.
The die preferably comprises two body portions in opposition with a spacer or shim therebetween. In such cases, channel(s) provided in the shim define flow path(s) to the front of the die. At the front of the die, at least one open mouth, preferably formed by substantially parallel roof and floor portions, terminates in lips that are preferably perpendicular to the roof and floor portions. Such a mouth/lip arrangement may also be provided without the use of a shim by integrating the supply channels in the die.
Each of the elements of the die may be provided by separate pieces so long as they are stacked in a substantially horizontal manner when in use. So long as no drain for coating solution is introduced by the arrangement of elements making up the die, the configuration may be varied or characterized otherwise. However produced or characterized, the mouth and lip aspects of the die enable laying down a precision coating of solution.
The present invention includes systems comprising any of these features described herein. Furthermore, complete manufacturing systems including production systems and coated product form aspects of the present invention. Product may take the form of coated webbing or completed test strips. Methodology described herein also forms part of the invention.